Image processing system, image processing method, and storage medium

ABSTRACT

A color conversion is performed to convert a data of a pixel of black in an object as determined to be a mask into a pixel data of composite black, and convert a data of a pixel of black in an object as not determined to be any mask into a pixel data of composite black or real black, and a set of pixel data of an object as color-converted is operated and processed as a source.

FIELD OF THE INVENTION

The present invention relates to an image processing, and in particular,to an image processing before a raster operation.

DESCRIPTION OF RELATED ART

As disclosed in Japanese Patent Application Laid-Open Publication No.2006-135936, there is a raster operation (referred herein sometimes to“ROP”) known in the art of image processing system, as an operationbetween a source as a set of pixel data to be drawn and a destination asa set of pixel data to be output to draw an image, for reflection ofresults of the operation on associated pixel data. The raster operationemploys a logic operation or the like to permit a facilitated expressionof superimposed objects of an image to be drawn.

Some objects of images to be drawn may be locally transparent. An objecthaving such a transparent region may be superimposed on another objectand be processed as a source by a simple logic operation. Here thetransparent region may be deemed as opaque white, and a correspondingregion of the other object may be hidden behind the transparent region.

For avoidance of that, there is a technique in use for a transparentregion to see an underlying object therethrough. Here a combination of amask corresponding to the transparent region and a real image isemployed to implement a double-staged rater operation. In this methodthe mask is filled with black in all area except for a transparentregion and is combined with a destination to perform an AND operation inbetween. And then the result is combined with the real image filled withblack in a region corresponding to the transparent region to perform anOR operation in between, whereby an image seeing the underlying objectthrough the transparent region is obtained.

SUMMARY OF THE INVENTION

ROP-oriented systems such as a printer deriver and a printer controllerhave configurations to: input a set of an object including a set ofimage data expressed in an RGB form and an ROP code designating anoperation from an associated operating system, application, or the like;convert the data format into a CMYK form; and perform an operation inaccordance with the ROP code.

For a printing in CMYK form, associated pixels are typically expressedin a binarized CMYK form, affording to use two expressions of blackpixel, so-called a “real black” such that C=M=Y=1, K=0, and so-called a“composite black” such that C=M=Y=K=0. As used herein, ‘0’ is to dot and‘1’ not to dot. In general, the real black is better in reproduction andis free of anxiety about color shift, and so it is desirable in mostcases to express black pixels of object in real black.

For black pixels in a mask, the logic operation in combination with adestination is performed for any color of C, M, Y, and K, each of whichis to be ‘0’. Therefore, as shown in FIGS. 9A and 9B, for black pixelsin object all expressed in real black, each data set of C, M, and Y getsinactive as a mask. FIGS. 9A and 9B are illustrations for explanation ofcolor separation of a pixel data of composite black and a pixel data ofreal black.

To this point, it is an object of the present invention to provide atechnique allowing for an improved color reproduction in a rasteroperation of image drawing objects having a transparent region withoutlosing a mask function.

To achieve the object described, according to a first aspect of thepresent invention, an image processing system is adapted to input asequence of image drawing objects each respectively including a set ofdata on pixels of a cell of color image and a raster operation code,hold a set of pixel data of an arbitrary object to be processed as asource for a raster operation in accordance with an associated rasteroperation code, and hold a set of pixel data of an object to be outputas a destination, and comprises a determiner configured to determine ann-th input object (n being an integer) to be a mask, as the n-th inputobject fills a first criterion as requisite for the n-th input object tobe determined as a mask and an n+1-th input object fills a secondcriterion as sufficient for a presumption for the n+1-th input object tobe masked by the n-th input object, a converter configured for a colorconversion to convert a data of a pixel of black in an object asdetermined to be a mask into a pixel data of composite black, andconvert a data of a pixel of black in an object as not determined to beany mask into a pixel data of composite black or real black, and aprocessor configured to operate and process as a source a set of pixeldata of an object as color-converted.

According to a second aspect of the present invention, in the imageprocessing system according to the first aspect, the converter isconfigured to convert a pixel data of a first pixel of black in an m-thinput object (m being an integer) as not determined to be any mask intoa pixel data of composite black, as the first pixel corresponds in pixelposition to a pixel of white in an m−1-th input object as determined tobe a mask, and convert a pixel data of a second pixel of black in them-th input object into a pixel data of real black, as the second pixelcorresponds in pixel position to a pixel of color else than white in them−1-th input object as determined to be a mask,

According to a third aspect of the present invention, in the imageprocessing system according to the first aspect, the first criterioncomprises each pixel in the n-th input object being black or white, anda raster operation code of the n-th input object including:

“D (destination) AND S (source)”;

“D OR (NOT S)”;

“D AND (NOT S)”; or

“D OR S”.

According to a fourth aspect of the present invention, in the imageprocessing system according to the third aspect, the second criterioncomprises a drawing region of the n+1-th input object lapping over adrawing region of the n-th input object, and a raster operation code ofthe n+1-th input object having to the raster operation code of the n-thinput object a correspondence relationship of:

“D OR S” to “D AND S”;

“D AND S” to “D OR (NOT S)”;

“D OR S” to “D AND (NOT S)”; or

“D AND S” to “D OR S”.

According to a fifth aspect of the present invention, in the imageprocessing system according to the first aspect, the processor comprisesa binarizer configured to binarize a pixel data of the object ascolor-converted by prescribed colors.

According to a sixth aspect of the present invention, an imageprocessing method comprises inputting a sequence of image drawingobjects each respectively including a set of data on pixels of a cell ofcolor image and a raster operation code, holding a set of pixel data ofan arbitrary object to be processed as a source for a raster operationin accordance with an associated raster operation code, holding a set ofpixel data of an object to be output as a destination, determining ann-th input object (n being an integer) to be a mask, as the n-th inputobject fills a first criterion as requisite for the n-th input object tobe determined as a mask, and an n+1-th input object fills a secondcriterion as sufficient for a presumption for the n+1-th input object tobe masked by the n-th input object performing a color conversion toconvert a data of a pixel of black in an object as determined to be amask into a pixel data of composite black, and convert a data of a pixelof black in an object as not determined to be any mask into a pixel dataof composite black or real black, and operating and processing as asource a set of pixel data of an object as color-converted.

According to a seventh aspect of the present invention, a storage mediumcomprises a stored program to have a computer execute an imageprocessing method according to the sixth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an image processor according to anembodiment of the present invention.

FIG. 2 is a block diagram of a color converter and a binarizer of theimage processor of FIG. 1.

FIG. 3 is a flowchart of actions of the image processor of FIG. 1.

FIGS. 4A to 4G provide a set of illustrations for explanation of rasteroperations using an object with a transparent region.

FIGS. 5A to 5C provide a set of illustrations for explanation of rasteroperations using an object with a transparent region.

FIG. 6 is an illustration of a mask object.

FIG. 7 is an illustration of a real-image object.

FIGS. 8A and 8B provide a set of illustrations for explanation of rasteroperations using an object with a transparent region.

FIGS. 9A and 9B provide a set of illustrations for explanation of colorseparation of a pixel data of composite black and a pixel data of realblack.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will be described the preferred embodiments of the presentinvention with reference to the drawings. FIG. 1 is a block diagram ofan image processor 10 as an image processing system according to anembodiment. The image processor 10 is adapted to sequentially input aset of image drawing objects constituting a page and to output a set ofbinarized data of the page. The image processor 10 is adaptive as aprinter driver or printer controller for instance.

Each image drawing object is a data set as output from an operatingsystem, application, or the like, and includes: a set of image data ofthe object represented in an RGB form; and an ROP code indicating anoperation in an associated ROP process. The set of binarized data is adata set representing constituent pixels of a page in terms of bits of aCMYK form.

The image processor 10 is made up by a processing unit 100 such as a CPUand a memory 200 with a bus 300 for their connections. The processingunit 100 includes: a mask determiner 100 for a decision to determinewhether or not an input image drawing object is a mask; a colorconverter 120 for converting a set of image data of RGB form into a setof image data of CMYK form by use of a lookup table or the like; abinarizer 130 for binarization of CMYK data by way of a pattern dither,error diffusion, etc; and an ROP operator 140 for raster operation. Eachcomponent described may be implemented as software for execution ofprograms or hardware using a wired logic or the like.

The memory 200 has storage areas formed therein, including: adestination area 210 for storing a series of sets of image data to bedrawn each as a destination of an associated raster operation; a sourcearea 220 for storing a series of sets of image data of input objectseach as a source to be raster-operated; a mask buffer area 230 fortemporary storage of a set of image data of an object as provisionallydetermined to be a mask by the mask determiner 110; an ROP code area 240for storing a series of ROP codes of input image drawing objects; and aworking area 250 for other operations and processes.

FIG. 2 illustrates, in a block diagram, a combination of the colorconverter 120 and the binarizer 130. As illustrated in FIG. 2, accordingto this embodiment, the color converter 120 is adapted for a colorconversion of a set of image data of object composed of data on R, G,and B of eight bits each into a set of image data composed of data on C,M, Y, and K of eight bits each. The binarizer 130 is adapted for asuccessive binarization into a set of image data composed of data on C,M, Y, and K of one bit each. The ROP operator 140 is adapted for araster operation after the binarization. Such the raster operationfollowing binarization allows for a reduced occupation or saved capacityin the memory 200, and an enhanced processing rate relative to a rasteroperation of multi-value data, whereas the present invention may beimplemented for application to a multi-value raster operation as well.

The present invention is in no way restricted to a raster operation ofimage data in a CMYK form, and may be implemented for applications to,e.g., a printing using a pair of colors such as red and black, as wellas to other forms of color expression. In particular, it has aneffective application to a form including a specific color, such asblack, that can be expressed in different manners. In such cases also, abinarization of each color may well be performed before a rasteroperation, allowing for a reduced occupation or saved capacity in thememory 200, and an enhanced processing rate.

There will be described below a typical method of handling an objectwith a transparent region in a raster operation by the ROP operator 140.The description is done with an example that a rectangular object 30illustrated in FIG. 4B with a star depicted amid a surroundingtransparent region is superimposed on a background image 20 illustratedin FIG. 4A for preparation of a superimposed image 40 illustrated inFIG. 4C such that the background image 20 is seen through thetransparent region surrounding the star.

There are two logic operations “AND” and “OR” for use raster operation.Table 1 lists results of AND operations and OR operations between adestination D and a source S, letting black be ‘0’ and white be ‘1’. Aswill be seen from the results, through AND operations, black pixels inthe source are rendered black, and white pixels in the source havevalues of corresponding pixels in the destination held as they are.Through OR operations, white pixels in the source are rendered white,and black pixels in the source have values of corresponding pixels inthe destination held as they are.

TABLE 1 Logical AND and OR operations between D (destination) and S(source) D S D AND S D OR S 0 (black) 0 (black) 0 (black) 0 (black) 1(white) 0 (black) 0 (black) 1 (white) 0 (black) 1 (white) 0 (black) 1(white) 1 (white) 1 (white) 1 (white) 1 (white)

A simple pixel-wise OR operation between the background image 20 and heobject 30 with a transparent region would have resulted in such asuperimposed image 40 x as illustrated in FIG. 4D failing to see thebackground image 20 through the transparent region, where it is deleted.A simple pixel-wise AND operation between the background image 20 andthe object 30 with a transparent region would have resulted in such asuperimposed image 40 y as illustrated in FIG. 4E in which thebackground image 20 fills in an associated region of the object 30.

To this point, for an object of image 30 that has a transparent region,the operation employs a combination of an object prepared as a mask 30 mcorresponding to the above-noted object 30, as it is blacked out in allarea except for the transparent region, as illustrated in FIG. 4F, andan object prepared as an actual or real image 30 a corresponding to theobject 30, as it is blacked out in the transparent region, asillustrated in FIG. 4G. The object of mask 30 m, as well as the objectof real image 30 a, may be prepared by an operating system, or by anapplication, as circumstances require. In the embodiment, pixels havebinary values set to ‘0’ for black and ‘1’ for white, for comprehensionwith ease. For the processing of CMYK form, a raster operation isperformed for each color, and the mask-filling black should beC=M=Y=K=0. For raster operations in a multi-value state, such as aneight-bit form, not one bit each of CMYK, each bit should be ‘0’.

Description is now made of associated operations. First as illustratedin FIG. 5A, using the background image 20 as a source S, an operation ofD=S is performed. The background image 20 is thereby set as adestination. Next, as illustrated in FIG. 5B, using the mask 30 m as asource, an operation of D AND S is performed. Through the AND operation,black pixels in the source are rendered black, and white pixels in thesource have values of corresponding pixels in the destination held asthey are, whereby set is a destination as a superimposed image 40 a inwhich a black region of the mask 30 m is superimposed on the backgroundimage 20. Then, using the real image 30 a as a source, an operation of DOR S is performed. Through the OR operation, white pixels in the sourceare rendered white, and black pixels in the source have values ofcorresponding pixels in the destination held as they are, wherebyobtained is a superimposed image 40 seeing the background image 20through a transparent region surrounding the star. It is noted thatoperations and object combinations are in no way restricted to thosedescribed, and the superimposed image 40 is obtainable by differentcombinations, as well.

Description is now made of actions in a process of the image processor10 in this embodiment, with reference to a flowchart of FIG. 3. Thisprocess is for a sequential reading of a series of image drawing objectsconstituting a page, to output a binary page data. Each image drawingobject is assumed as including a set of image data and an ROP code, andcarrying no effective information to define whether it is a mask or areal image else than the mask. Object image data else than mask isreferred herein sometimes to a usual data.

At a step S101, the image processor 10 reads an image drawing object, asit is input from an associated operating system, application, or thelike. Read object has a set of image data and an ROP code. The imageprocessor 10 stores the image data set in the source area 220, and theROP code in the ROP code area 240.

At a decision step S102, it is determined whether or not the mask bufferarea 230 has a data stored therein. The mask buffer area 230 is providedas an area for temporary storage of an image data set of an object astemporarily determined to be a mask by the mask determiner 110. If adata is stored in the mask buffer area 230, this state means apreviously read image drawing object has been temporarily determined tobe a mask, that is, an image data set of the previous object may be anobject image data to be processed as a mask.

As a result, unless a data is stored in the mask buffer area 230 (NO atthe step S102), the flow goes to another decision step S103 totemporarily determine whether or not the currently read object is amask. The read object is assumed as carrying no direct information todefine whether it is a mask or not, and the possibility of its being amask is determined in the following manner.

There is a first criterion to be filled, including two conditions beinga condition 1 and a condition 2 to be both met to temporarily determinethe currently read object to be a mask:

Condition 1: each pixel of the object image data set to be black orwhite. If the object image data is expressed in an RGB form of eightbits each, the white is R=G=B=255, and the black is R=G=B=0; and

Condition 2: the ROP code to be “D AND S”, “D AND S”, “D OR /S”, or “DOR S”, where ‘/’ denotes “NOT”.

This is for a temporary determination, not a final, on presence orabsence of the possibility of being a mask.

It is noted that the mask determination may employ ROP codes complyingwith XOR logic.

As a result, if the first criterion is filled (YES at the step S103),the object image data set is stored in the mask buffer area 230. Inother words, at this stage, there being no final determination as to ifthe currently read object be a mask the data set is temporarily storedin the mask buffer area 230, without entering an image drawing process.

On the other hand, unless the first criterion is filled (NO at the stepS103), the control flow goes to a step S105 to have the object imagedata set processed as a usual data for image drawing. More specifically,the format of image data set is converted from an RGB form to a CMYKform, where black pixels are converted to real black being C=M=Y=1, K=0.The image to be drawn is thereby given an enhanced reproducibility ofblack. After binarization, the data set is to be raster-operated inaccordance with an associated ROP code.

In either case, at a step S112, it is determined if the process for acurrent page is completed. If it is completed (YES at the step S112),the flow goes to a step S113 to output a binary page data composed of aseries of image data sets having been accumulated till then in thedestination area 210, before the present process goes to an end. Unlessthe process for the current page is completed (NO at the step S112), theflow again goes to the step S101 to repeat the process described.

As a result of determination by a check for a stored data in the maskbuffer area 230 at the step S102, if the mask buffer area 230 has astored data (YES at the step S102), the flow goes to another decisionstep S106, where it is determined whether or not the image data set ofthe currently read object is a real image of the stored data in the maskbuffer area 230. It is noted that the data set of the object of realimage is to be operated together with a data set of an object of mask todraw an image that has a transparent region as described. As will bedescribed later, the mask buffer area 230 is to be cleared after aprocess based on the above-noted determination, and any data stored inthe mask buffer area 230 should be a set of image data of a previouslyread image drawing object.

The image drawing object is assumed as carrying no direct information toknow if its data set represents a real image, so the determination as towhether or not the data set of the currently read object represents areal image of a data set stored in the mask buffer area 230 is made inthe following manner.

There is a second criterion to be filled, including two requirementsbeing a condition 3 and a combination of four alternate conditions 4 to7, to be both met to finally determine the data set of the currentlyread object to represent a real image of a data set stored in the maskbuffer area 230.

Condition 3: an image drawing region of a set of image data of objectstored in the mask buffer area 230 being identical in terms of pixelpositions to an image drawing region of a set of image data of thecurrently read object. For instance, the two image data sets may bedetermined as having an identical image drawing region if they have anidentical start point for image drawing and an identical image drawingsize;

Condition 4: an ROP code of the currently read object being “D OR S”,subject to a previously read object having an ROP code of “D AND S” andthe image data set thereof stored in the mask buffer area 230;

Condition 5: an ROP code of the currently read object being “D AND S”,subject to a previously read object having an ROP code of “D OR /S (i.e.NOT S)” and the image data set thereof stored in the mask buffer area230;

Condition 6: an ROP code of the currently read object being “D OR S”,subject to a previously read object having an ROP code of “D AND /S(i.e. NOT S)” and the image data set thereof stored in the mask bufferarea 230; and

Condition 7: an ROP code of the currently read object being “D AND S”,subject to a previously read object having an ROP code of “D OR S” andthe image data set thereof stored in the mask buffer area 230.

As a result, if the image data set of the currently read object isdetermined as representing a real image of the image data set of objectstored in the mask buffer area 230 (YES at the step S106), it can beconcluded that the image data set of object stored in the mask bufferarea 230 should be a mask data to be combined with the real image dataset, and the flow goes to a step S107 to draw the image data set ofobject stored in the mask buffer area 230 as a mask.

More specifically, the format of the stored image data set is convertedfrom an RGB form to a CMYK form, where black pixels are converted tocomposite black being C=M=Y=K=0. This data set is thereby allowed towork as a mask in raster operation. After binarization, the data set isto be raster-operated in accordance with an associated ROP code.

At a step S108, the image data set of the currently read object isprocessed as a usual data to draw an image. This image drawing processis varied in accordance with a corresponding one of the above-notedconditions 4 to 7.

For the condition 4 as correspondent, the format of image data of thecurrently read object is converted from an RGB form to a CMYK form,where pixel data of the currently read object are processed in thefollowing manner in accordance with values of pixels in correspondentpositions in an associated mask (e.g. the mask 30 m in FIG. 5B). Pixelvalues of mask can be got by reference to the image data set stored inthe mask buffer area 230.

That is, for those black pixels in the currently read object wheretopixels in corresponding positions in the mask (e.g. mask 30 m in FIG.5B) have values representing a background (white), i.e., C=Y=M=K=1,their pixel values are converted to C=M=Y=K=0 being composite black.They are thus allowed to see through by raster operation. And, afterbinarization, at a sub-step S108 a, a raster operation is performed inaccordance with an associated ROP code (D OR S).

Supplemental description will be made with reference to FIGS. 5A to 5Cas an example. The mask 30 m in FIG. 5B is an entirety of mask dataincluding a transparent white region. The real image 30 a in FIG. 5C hasa peripheral black region to be transparent. As the condition 4 (for theROP code of the currently read object to be “D OR S”) is met, the ORoperation between a region 40 a of the destination D and the transparentregion of the real image 30 a (the black region surrounding the star)gives a result illustrated at 40 in FIG. 5C (as the white region of themask is transparent), and in the real image 30 a, the peripheral regionto be transparent about the star is made black. In other words, in orderfor the mask function to be effective for C, M, Y, and K, black pixelsin the currently read object have their C, M, Y, and K values rendered‘0’. For the OR operation, respective values of destination D are heldas they are if the value of source S is ‘0’ (black), and for thetransparent region 40 a, values of destination D are held to be correct.

On the other hand, for those black pixels in the currently read object(e.g. inside the star of the real image 30 a in FIG. 5C) whereto pixelsin corresponding positions in the mask (e.g. mask 30 m in FIG. 5B) havevalues representing a filled region (with black), i.e., C=Y=M=K=0, theirpixel values are converted to C=M=Y=1, K=0 being real black. The imageto be drawn is thus allowed to have an enhanced black reproducibility.After binarization, a raster operation is performed in accordance withan associated ROP code (D OR S).

Additional description will be made with reference to FIGS. 5A to 5C asan example. The mask 30 m in FIG. 5B has a star-shaped black region as aregion to be finally over-written by real data. For the OR operation,pixel values of any region of destination D are rewritten to values ofsource S if the region is black (0). To this point, it is desirable toshow the region by real black, and associated pixel values are processedto be C=M=Y=1, K=0. As the region desired to overwrite is set to ‘0’ asdescribed, such real black values can be OR-operated to provide acorrect result.

For the condition 6 to be correspondent, at the sub-step 108 a, likeprocess to the condition 4 is applicable. However, in this case, in themask 30 m of FIG. 4F employed for the condition 4, colors of the blackand white regions are mutually inverted, so such a mask 31 m asillustrated in FIG. 6 is used as a mask data.

For the condition 5 to be correspondent, first, such a real image 32 aas illustrated in FIG. 7 is used as a real image data, in place of thereal image 30 a illustrated in FIG. 4G In other words, the real image tobe used has a transparent region expressed in white. For mask data, themask 30 m illustrated in FIG. 4F is applicable.

Therefore, in the process at the step S107, using the background 20 as adestination D and the mask 30 m as a source S as illustrated in FIG. 8A,there is made an operation of “D OR /S (i.e. NOT S)” to the mask for thecondition 5, obtaining an image 42 a.

Then, in the process at the step S108, the format of image data of thecurrently read object is converted from an RGB form to a CMYK form.Along therewith, at a sub-step S108 b, pixel values of black in theobject are converted to C=M=Y=1, K=0 being real black. The image to bedrawn is thus allowed to have an enhanced black reproducibility. Afterbinarization, a raster operation is performed in accordance with anassociated ROP code (D AND S). In other words, there is no need toswitch the manner of conversion of black depending on a pixel value at acorresponding location in the mask, thus allowing for a uniformconversion to real black without exception. It therefore is possible toobtain such a superimposed image 40 as illustrated in FIG. 8B, where thebackground image 20 is seen through the transparent region surroundingthe star.

For the condition 7 to be correspondent, at the sub-step 108 b, likeprocess to the condition 5 is applicable. However, in this case, in themask 30 m of FIG. 4F employed for the condition 5, colors of the blackand white regions are mutually inverted, so such a mask 31 m asillustrated in FIG. 6 is used as a mask data.

On the contrary, as a result of determination in the process at the stepS106 as to whether or not the image data set of the currently readobject is a real image of the data set of object stored in the maskbuffer area 230, unless the image data set of the currently read objectis determined to be a real image of the data set of object stored in themask buffer area 230 (NO at the step S106), it is possible to concludethat the data set of object stored in the mask buffer area 230 is notany mask. Therefore, at a step S109, the data set of object stored inthe mask buffer area 230 is processed as a usual data to draw an image.

More specifically, the format of image data set is converted from an RGBform to a CMYK form, where black pixels are converted to real blackbeing C=M=Y=1, K=0. The image to be drawn is thereby given an enhancedreproducibility of black. After binarization, the data set is to beraster-operated in accordance with an associated ROP code.

At a step S110, the image data set of the currently read object isprocessed as usual data to draw an image. More specifically, the formatof image data set of the object is converted from an RGB form to a CMYKform, where black pixels are converted to real black being C=M=Y=1, K=0.The image to be drawn is thereby given an enhanced reproducibility ofblack.

In either case, after binarization, a raster operation is performed inaccordance with an associated ROP code. Thereafter, at a step S111, themask buffer area 230 is cleared.

At the step S112, it is determined if the process for the current pageis completed. If it is completed, the flow goes to the step S113 tooutput a binary page data composed of a series of image data sets havingbeen accumulated till then in the destination area 210, before thepresent process goes to an end. Unless the process for the current pageis completed, the flow again goes to the step S101 to repeat the processdescribed.

As will be seen from the foregoing embodiments, according to the presentinvention, black color of pixels in an object as determined to be a maskis converted to composite black, and that of pixels in an object asdetermined not to be any mask is converted to real black, thus allowingfor an improved color reproduction in a raster operation of imagedrawing objects having a transparent region without losing a maskfunction.

This application is based on the Japanese Patent Applications No.2008-076585, filed on Mar. 24, 2008, the entire content of which isincorporated by reference herein

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposes, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

1. An image processing system adapted to input a sequence of imagedrawing objects each respectively including a set of data on pixels of acell of color image and a raster operation code, hold a set of pixeldata of an arbitrary object to be processed as a source for a rasteroperation in accordance with an associated raster operation code, andhold a set of pixel data of an object to be output as a destination, thesystem comprising: a determiner configured to determine an n-th inputobject (n being an integer) to be a mask, as the n-th input object fillsa first criterion as requisite for the n-th input object to bedetermined as a mask, and an n+1-th input object fills a secondcriterion as sufficient for a presumption for the n+1-th input object tobe masked by the n-th input object; a converter configured for a colorconversion to convert a data of a pixel of black in an object asdetermined to be a mask into a pixel data of composite black, andconvert a data of a pixel of black in an object as not determined to beany mask into a pixel data of composite black or real black; and aprocessor configured to operate and process as a source a set of pixeldata of an object as color-converted.
 2. The image processing systemaccording to claim 1, wherein the converter is configured to convert apixel data of a first pixel of black in an m-th input object (m being aninteger) as not determined to be any mask into a pixel data of compositeblack, as the first pixel corresponds in pixel position to a pixel ofwhite in an m−1-th input object as determined to be a mask, and converta pixel data of a second pixel of black in the m-th input object into apixel data of real black, as the second pixel corresponds in pixelposition to a pixel of color else than white in the m−1-th input objectas determined to be a mask.
 3. The image processing system according toclaim 1, wherein the first criterion comprises a pair of first andsecond conditions, wherein the first condition is that each pixel in then-th input object is black or white, and the second condition is that araster operation code of the n-th input object is: “D (destination) ANDS (source)”; “D OR (NOT S)”; “D AND (NOT S)”; or “D OR S”.
 4. The imageprocessing system according to claim 3, wherein the second criterioncomprises a pair of third and fourth conditions, wherein the thirdcondition is that a drawing region of the n+1-th input object overlaps adrawing region of the n-th input object, and the fourth condition isthat a raster operation code of the n+1-th input object has acorrespondence relationship to the raster operation code of the n-thinput object as follows: “D OR S” to “D AND S”; “D AND S” to “D OR (NOTS)”; “D OR S” to “D AND (NOT S)”; or “D AND S” to “D OR S”.
 5. The imageprocessing system according to claim 1, wherein the processor comprisesa binarizer configured to binarize a pixel data of the object ascolor-converted by prescribed colors.
 6. An image processing method,comprising: inputting a sequence of image drawing objects eachrespectively including a set of data on pixels of a cell of color imageand a raster operation code; holding a set of pixel data of an arbitraryobject to be processed as a source for a raster operation in accordancewith an associated raster operation code; holding a set of pixel data ofan object to be output as a destination; determining an n-th inputobject (n being an integer) to be a mask, as the n-th input object fillsa first criterion as requisite for the n-th input object to bedetermined as a mask, and an n+1-th input object fills a secondcriterion as sufficient for a presumption for the n+1-th input object tobe masked by the n-th input object; performing a color conversion toconvert a data of a pixel of black in an object as determined to be amask into a pixel data of composite black, and convert a data of a pixelof black in an object as not determined to be any mask into a pixel dataof composite black or real black; and operating and processing as asource a set of pixel data of an object as color-converted.
 7. Anon-transitory storage medium comprising a stored program to have acomputer execute an image processing method according to claim 6.